1. Field of the Invention
The present invention is in the field of multi-function valves. More particularly, the present invention relates to a multi-function valve having particular utility in the performance of open-heart surgery. Still more particularly, the present invention relates to a multi-function valve useful during open heart surgery for controlling aspirated fluid flow from the left ventricle of the heart to an aspiration pump by controlling the level of aspiration suction applied at the heart, for preventing inadvertent reverse flow of fluid to the heart, for safely and controllably venting reverse flow positive pressure which would cause such reverse flow of fluid to the heart, and for controlling inlet positive pressure at the control valve, which inlet positive pressure causes conventional control valves to undesirably weep patient's blood into the operating room environment.
2. Related Technology
In the performance of open heart surgery, generally the heart is bypassed and the patient's blood circulation is maintained by use of a heart-lung machine. However, a certain amount of blood finds its way into the left ventricle of the heart. Unless this blood is removed, the left ventricle of the heart is distended and resuscitation of the heart at the conclusion of the procedure is made more difficult or impossible.
Accordingly, some physicians insert a drain tube into the left ventricle and use a positive-displacement aspiration pump to remove the accumulated blood. The speed of operation of such a pump positive-displacement aspiration pump determines the rate at which the pump will aspirate blood from the left ventricle. An insufficient rate of aspiration can still allow blood to accumulate in the left ventricle. On the other hand, an excessive aspiration rate may cause the drain tube to suck against the heart tissues, thereby causing trauma. One former but currently unpopular solution to this problem is to have the speed of the positive-displacement aspiration pump controlled by a technician. However, this solution requires additional operating room personnel and requires additional communication from the physician to the technician.
Another conventional and currently common solution is to use a positive-displacement aspiration pump, for example, a pump of the roller type, and to control its operational speed to a constant level throughout the surgical procedure. In order to control the level of aspirating suction applied to the left ventricle of the heart during the surgical procedure, a pre-set negative pressure relief valve is generally disposed in the suction line between the heart and the positive-displacement aspiration pump. This valve controls the suction applied to the heart by venting ambient air into the suction line downstream of the valve.
Such a suction control valve may also include a check valve safety feature which prevents reverse flow of fluid toward the heart in the event that plumbing is connected incorrectly during the procedure, or should the aspiration pump be operated in reverse, or should the aspiration pump be stopped with a pressurized reservoir downstream of the pump, for example, causing a positive pressure reverse flow toward the heart.
However, such a reverse flow positive pressure check valve function results in the blood aspiration plumbing, which has been designed to withstand suction, being exposed to an unregulated positive pressure. If the reverse flow positive pressure is high enough, the result can occasionally be the blowing off of an aspiration tube from a hose barb with resultant spray of blood into the operating room. In the event that the aspiration plumbing does not blow apart and the reverse flow positive pressure is high enough, the check valve may be overcome so that a catastrophic reverse positive pressure flows to the patient's heart.
Consequently, the control valve may also include a positive pressure venting feature which relieves such a reverse flow positive pressure. This feature insures that aspiration plumbing is not blown apart by such a reverse positive pressure. Also, this venting feature insures that the valve itself is not overcome by a sufficiently high reverse positive pressure such that fluid forces its way past the valve and to the heart.
Of course, operation of this safety feature of the control valve results in undesirable release of patient's blood into the operating room environment. That is, it is recognized that if the positive pressure were not controlled by venting at the control valve or elsewhere, it could possibly result in an uncontrolled venting of the pressure or a catastrophic reverse flow to the patient's heart. As explained above, aspiration tubing could be blown off of a hose barb fitting at a pressure higher than the venting pressure, and with resultant blood spray into the operating room totally without control of the direction or location of the resulting spray. Alternatively the check valve could be overcome so that fluid flows in reverse to the patient's heart. The former type of uncontrolled relief of an inadvertent positive pressure would be hazardous to operating room personnel. The latter type of reverse flow to the patient's heart could be fatal.
As a result, the controlled venting of blood at the control valve when necessary to vent such an unintended reverse positive pressure is an acceptable operational aspect of the conventional control valves. However, on the rare occasions when this positive pressure relief safety feature does function it is the result of an infrequent personnel or equipment error which could be catastrophic for the patient. Further, it is recognized that the venting of patient blood into the operating room environment because of a very infrequent reverse flow positive pressure of such magnitude is an accepted and necessary safety function. Preferably, the operating room personnel will have arrange the plumbing and the location of the control valve to minimize the risk from this venting function, should it occur. That is, the blood vented from the control valve is generally arranged at a controlled location near the floor of the operating room, and the venting is preferably is at a relatively low velocity so that spray and misting of blood into the operating room air is avoided.
Along the above line, U.S. Pat. No. 4,642,097, issued Feb.10, 1987, to G. Siposs, is believed to teach a control valve in which ambient air flow to a negative pressure vent port is controlled by a cammed sleeve member which is axially movable along a body of the control valve. A duck bill check valve member prevents reverse flow from the aspiration pump to the heart. Also, a sleeve-type positive pressure relief valve vents the passage downstream of the check valve member to ambient to prevent excessive pressure build up on that side of the control valve.
With a control valve as taught by the Siposs '097 patent, a physician or another person must adjust the control valve to set the venting level necessary to maintain a desired suction at the heart in view of the operating speed and pumping characterists of the aspiration pump. This set venting level continuously admits atmospheric air to the passage leading to the aspiration pump and results in an undesirably large amount of air being mixed with the aspirated blood. Also, the venting function is set and does not self-adjust in the event the speed of the aspiration pump, or other such factor which affects the level of suction at the heart, changes during the surgical procedure. Notably, this control valve uses a sleeve-type of positive pressure relief valve which does properly and controllably vent reverse flow positive pressure should such a pressure be applied to the valve. However, the direction of discharge and velocity of the vented blood are not predictable or controlled.
However, with conventional control valves in the event that the aspiration pump is stopped with the conduit between the heart and the control valve filled with fluid another deficiency comes to light. That is, the static fluid column pressure applies between the heart and the control valve applies a positive pressure at the inlet of the control valve, and can be enough to cause dripping and spitting of blood past the sleeve-type vent valve into the operating room environment. Such inlet positive pressure blood weeping from conventional control valves is much more common than blood venting because of inadvertent reverse positive pressure to the control valve. Because this unintended venting of blood from inlet positive pressure to the control valve is so common, it is especially undesirable in the present medical environment. That is, the present medical environment includes risk factors for exposure to AIDS and Hepatitis through blood contact. As is well known, the present medical environment emphasizes all possible controls over exposure of operating room and other medical personnel to patient's blood.
A later U.S. Pat. No. 4,758,224, issued Jul. 19, 1988, also to G. Siposs, is believed to teach a similar control valve which also uses a duck bill check valve member, and a sleeve valve positive pressure relief valve. However, the control valve taught by this patent uses an umbrella-type of negative pressure relief valve so that the physician does not need to adjust the valve to control the maximum suction level applied to the patient's heart. This umbrella type valve is disposed in a chamber situated laterally of and communicating with the main fluid flow path through the valve.
With a control valve as set forth in the Siposs '224 patent, the disadvantage outlined above with respect to undesirable loss of blood into the operating room environment still exists. That is, the sleeve valve type of positive pressure relief valve can still be forced open simply by the liquid column pressure of the blood in the aspiration conduit if the aspiration pump is stopped with this conduit full of liquid. The necessary safety factor of a positive pressure relief function with this valve also presents the undesirable possibility that patient's blood may be released into the operating room environment from the control valve.
Yet another conventional control valve is set out in U.S. Pat. No. 4,725,266, issued Feb. 16, 1988, also to G. Siposs. The Siposs '266 patent is believed to teach a control valve in which a duck bill valve member serves as both a check valve allowing fluid flow only toward the aspirating pump, and also includes a circumferentially and axially extending resilient cylindrical body portion which sealingly cooperates with the valve body at a negative pressure relief port. When the negative pressure in the conduit leading to the aspiration pump reaches a predetermined maximum, the cylindrical portion of the duck bill valve member yields to allow introduction of ambient air and limits the maximum suction applied to the patient's heart.
However, the control valve according to the '266 patent still uses the familiar sleeve type valve for positive pressure relief so that the disadvantage of unintended release of patient's blood into the operating room from the control valve because of an inlet positive pressure is still present.
Still another control valve is seen in two related U.S. Pat. Nos., 4,502,502; and 4,671,786, issued Mar. 5, 1985, and Jun. 9, 1987, respectively, to J. Krug. These control valves use the familiar duck bill valve member to perform the check valve function. Also, the negative pressure relief valving function is performed by an umbrella valve member disposed in a lateral chamber like that seen in the '224 patent to Siposs. However, the positive pressure relief valving function is performed by a second umbrella valve controlling communication outwardly from this lateral chamber to ambient.
The control valves taught by the Krug '502, and '786 patents also suffer from the undesirable weeping or dribbling of patient's blood into the operating room environment because of an inlet positive pressure created by a fluid column pressure in the aspiration tubing, as was discussed earlier. That is, the choice of an umbrella type of positive pressure relief valve does not eliminate this problem of all of the conventional control valves discussed herein.
The conventional control valves all accept the necessary controlled venting of blood which could result in the unlikely event of incorrect plumbing connection, reverse operation of the aspiration pump, or stopping of the pump with a pressurized reservoir downstream of the pump causing pressurized blood backflow. However, these occurrences are rare, and the safety function of the valve is necessary to prevent catastrophic injury to the patient.
On the other hand, the spitting of blood into the operating room environment from the positive pressure vent valve simply because of fluid column pressures in the connecting tubing is a common occurrence, and is objectionable because of its frequency. This blood on the operating room floor at the very least presents an undesirable mess and cleaning burden in the operating room, as well as a risk that personnel will slip and fall on the blood. Moreover, the risk of AIDS or Hepatitis exposure because of contact with patient's blood can not be ignored. A positive pressure vent valve should not allow this unintended release of patient's blood caused by a positive fluid pressure communicating to the inlet of the valve.
Also, the existence of a lateral chamber on the valves of Krug (and on the '224 valve of Siposs) which requires a laterally projecting boss within which to define this lateral chamber, undesirably presents a projection on the exterior of the control valve. Of course, this projection is a hindrance to handling of the control valve and its attached tubing in the operating room environment because this attached tubing and other nearby tubing as well as wiring and instrument cables, for example, may catch on the projection form the control valve. All of the discussed control valves also suffer from an undesirable complexity in their construction, with an excessive parts count.
Finally, the conventional control valves seem by their designs to accept the inevitability of unpredictable venting of patient's blood if a reverse flow positive pressure level applied to the valve reaches the venting pressure level. That is, this safety venting feature is accepted as necessary, but the consequences of this feature operating are not dealt with in the designs of conventional control valves. A control valve should allow this venting only in a fashion best preserving safety for surrounding operating room personnel.